© Copyright by the National Institute of Public Health - National Institute of Hygiene
*Corresponding author: Maciej Szczotko, National Institute of Public Health - National Institute of Hygiene, Department of Environmental Hygiene, 24 Chocimska street, 00-791 Warsaw, Poland, tel.: +48 22 5421 382, fax: +48 22 5421 287, e-mail: mszczotko@pzh.gov.pl
ORIGINAL ARTICLE
EVALUATION OF SUSCEPTIBILITY OF POLYMER
AND RUBBER MATERIALS INTENDED INTO CONTACT
WITH DRINKING WATER ON BIOFILM FORMATION
Maciej Szczotko
*, Agnieszka Stankiewicz, Małgorzata Jamsheer-Bratkowska
National Institute of Public Health – National Institute of Hygiene,Department of Environmental Hygiene, Warsaw, Poland
ABSTRACT
Background. Plumbing materials in water distribution networks and indoor installations are constantly evolving. The application of new, more economical solutions with plastic materials eliminates the corrosion problems, however, do not fully protect the consumer against secondary microbial contamination of water intended for human consumption caused by the presence of a biofilm on the inner surface of materials applied. National Institute of Public Health - National Institute of Hygiene conducts research aimed at a comprehensive assessment of this type of materials, resulting their further marketing authorization in Poland.
Objectives. Evaluation and comparison of polymer and rubber materials intended to contact with water for the susceptibility to biofilm formation.
Materials and Methods. Plastic materials (polyethylene, polypropylene, polyvinyl chloride) and rubber compounds (EPDM, NBR), from different manufacturers were evaluated. The study was carried out on 37 samples, which were divided into groups according to the material of which they were made. The testing was conducted according to the method based on conditions of dynamic flow of tap water. The level of bioluminescence in swabs taken from the surface of the tested materials was investigated with a luminometer.
Results. Evaluation of plastic materials does not show major objections in terms of hygienic assessment. All materials met the evaluation criteria established for methodology used. In case of rubber compounds, a substantial part clearly exceeded the limit values, which resulted in their negative assessment and elimination of these materials from domestic market. Conclusions: High susceptibility to the formation of biofilm in the group of products made of rubber compounds has been demonstrated. Examined plastic materials, except for several cases, do not revealed susceptibility to biofilm formation, but application of plastics for distribution of water intended for human consumption does not fully protect water from secondary, microbiological contamination. Complete verification of plumbing materials including biofilm formation test before their introduction into the domestic market should be continued.
Key words: biofilm, plumbing materials, hygienic assessment, drinking water STRESZCZENIE
Wprowadzenie. Materiały wykorzystywane w sieciach wodociągowych oraz instalacjach wewnątrz budynków ulegają ciągłym zmianom. Wprowadzenie nowych bardziej ekonomicznych rozwiązań z zastosowaniem materiałów z tworzyw sztucznych eliminuje problemy związane z korozją, jednak nie zabezpiecza konsumenta przed wtórnym mikrobiologicznym zanieczyszczeniem wody przeznaczonej do spożycia powodowanym występowaniem biofilmu na wewnętrznej powierzchni rur i przewodów instalacyjnych. W Narodowym Instytucie Zdrowia Publicznego - Państwowym Zakładzie Higieny, prowadzone są badania mające na celu kompleksową ocenę tego typu materiałów, czego efektem jest wydawanie Atestów Higienicznych i dopuszczenie materiałów do obrotu na krajowym rynku.
Cel. Celem badań było porównanie i ocena materiałów z tworzyw sztucznych i gumy przeznaczonych do kontaktu z wodą do spożycia w zakresie ich podatności na tworzenie biofilmu.
Materiał i metody. Ocenie poddano materiały z różnych tworzyw sztucznych (polietylen, polipropylen, polichlorek winylu) oraz mieszanki gumowe pochodzące od różnych producentów. Badania wykonano dla 37 próbek, które zostały podzielone na grupy w zależności od rodzaju materiału z jakiego zostały wykonane. Badania prowadzone były zgodnie z metodyką własną, w dynamicznych warunkach przepływu wody, z wykorzystaniem urządzeń przepływowych (UPE). Za pomocą luminometru oznaczano poziom bioluminescencji w wymazach pobranych z powierzchni testowanych materiałów.
Wyniki. Ocena zbadanych materiałów z tworzyw sztucznych nie budziła większych zastrzeżeń pod względem higienicznym. Wszystkie materiały spełniały kryteria oceny określone w stosowanej metodyce badawczej, przy czym w kilku przypadkach oznaczone wartości były bliskie dopuszczalnego limitu. W przypadku mieszanek gumowych, w znacznej części stwierdzono wyraźne przekroczenia dopuszczalnych wartości, co skutkowało negatywną ich oceną oraz eliminacją tych materiałów zobrotu na krajowym rynku i możliwością ich wykorzystywania w kontakcie z wodą do picia. Wnioski. Wykazano znaczną podatność zbadanych produktów wykonanych z mieszanek gumowych na tworzenie się biofilmu. Materiały tworzywowe jak polietylen, polichlorek winylu i polipropylen, w znacznej większości nie wykazywały podatności na tworzenie się biofilmu, jednak ich zastosowanie do dystrybucji wody przeznaczonej do spożycia przez człowieka nie zabezpiecza jej w pełni przed wtórnym, mikrobiologicznym zanieczyszczeniem. W celu pełnej weryfikacji materiałów, przed ich wprowadzeniem na krajowy rynek, niezbędna jest dalsza ich ocena, z uwzględnieniem ich podatności na tworzenie się biofilmu.
Słowa kluczowe: biofilm, materiały instalacyjne, ocena higieniczna, woda przeznaczona do spożycia
INTRODUCTION
To the end of the 90’s of the last century the water supply systems in Poland were made of traditional materials like cast iron. They accounted for over 50% of the network and their technical condition due to the long lifetime (over 50 years) was of low quality [6]. However, these installations underwent successive repairs and upgrades, which entailed also change of materials used for this purpose. Since the beginning of the twenty-first century, it was observed a significant part of different material solutions like polyethylene (PE) and polyvinyl chloride (PVC) as well as an increasing use of a new generation of iron, so-called ductile iron [15, 16, 18].Currently, a significant share in the materials structure have pipes made of polymer materials (PE, PVC and others), which in some cases account for more than a half of the length of water supply networks. Generally, it can be said, that the water supply systems are built mainly of pipes made of cast iron, steel protected against corrosion usually by zinc, cementitious coating, PVC and PE. The pipes made of these materials account for about 90% of the network length [14, 17].In fact, it does not differ much from the standards in other European Union countries, as well as in the United States [25]. Plastics intended for use in the construction industry, especially those that can be applied in contact with drinking water must meet a number of strict requirements, not only technical like strength, flexibility and corrosion resistance, but primarily hygienic requirements, which apply to both, the physicochemical and microbiological parameters. All over the world the research is carried out focused on the acceptance of different products/ materials contacting with water intended for human consumption. These tests include so-called migration tests, performed to proof that the product/material has no negative influence on the quality of water contacting with it, and microbiological tests, including biofilm formation test. The hygienic assessments of products intended to contact with drinking water, are performed, among others, in the research centers in Germany (Gelsenkirchen Institute), France – Pasteur
Institute (ACS, AFNOR), Great Britain (WRAS), the Netherlands (KIWA), United States (NSF) and in many other countries, including Poland. Here in the National Institute of Public Health – National Institute of Hygiene (NIPH-NIH) hygienic assessment of materials is conducted during procedure of Hygienic Certificate issuing [3, 7, 12, 27, 30]. These centers conduct physicochemical and microbiological research, but only some of them carry out tests on microbial growth (biofilm formation test) for plastic and rubber products. Increasing number of metallic materials is replaced by polymer materials because of their high chemical resistance, good mechanical properties, which can be improved through the addition of modifiers like chalk, carbon black, chopped glass and elastomers. The use of polymer materials eliminates corrosion, known from occurrence in traditional materials (like cast iron, steel, concrete), provides channels tightness, even in critical situations (deflection instead of cracking) and guarantees proper attention to economy of the solutions. However, an attention should be payed to possible interactions that occur between the microorganisms present ce in tap water, and the material from which the network is made. In water environment, even inside the pipes and lines, which supply drinking water to consumer, there are two main forms of the presence of microorganisms. They can float freely in unbound form or bound with molecules of organic or inorganic matter suspended in water (planktonic form) or they can form complex agglomerates permanently colonizing the inner surfaces of the pipes - biofilm. Both these forms are not mutually exclusive, but microorganisms forming biological membranes are more frequently observed [22]. Biofilm, also defined as a biological membrane, is a three-dimensional, spatially complex structure, arising at the phases border, including different kinds of organic and inorganic surfaces contacting with water. The composition of the biofilm can vary. It can be a monoculture or a cluster of bacteria, very diverse morphologically and physiologically [4, 21]. Biofilm formed in plumbing installation is a very common phenomenon. Once produced, becomes very
difficult to remove and can cause many problems of technological importance by intensifying processes of biological corrosion and causing significant hydraulic losses inside the network and, above all, it may cause the health problems to consumer [13, 26]. Biofilm creates very favorable living conditions for microorganisms, provides them with a greater availability of nutrients [5, 23] and enables long-lasting and very stable settlement of diverse solid substrates, including construction materials contacting with water. Their presence has an impact on the quality of water delivered to the consumer. Frequent detachment of fragments of the mature biofilm inside water network causes ejection of a large number of bacteria, including pathogens and potential human pathogens such as Legionella pneumophila, Pseudomonas sp.,
Aeromonas sp., Campylobacter sp., Escherichia coli, Salmonella sp., Shigella sp. as well as microscopic
fungi [9, 10, 19, 29]. During exploitation of the water network, a permanent growth of the biofilm is observed, wherein the biomass of bacteria can reach 95% and only 5% of bacteria is present in the water in the form of so-called phytoplankton [20].
Therefore, it is important to choose the appropriate materials, which are used to build a water supply system at the first stage of its design. It enables avoiding the subsequent operational problems associated with the metabolic activity of microorganisms. Due to the extension of the hygienic certification procedure conducted in NIPH – NIH on biological laboratory tests allowing to perform complete assessment of the materials intended to contact with drinking water. It is possible to verify the quality of certified materials and to eliminate those, that due to the high susceptibility to biofilm formation, can cause secondary microbial contamination of water supplied to the consumer.
The aim of this study was the evaluation and comparison between some polymer materials and elements made of rubber intended to contact with drinking water on their susceptibility to biofilm formation.
MATERIALS AND METHODS
The study was carried out on 37 samples, which were divided into several groups according to the material of which they were made, enabled the general characteristics of each group.
Tested materials
During the research the following polymer materials were used: polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and rubber compounds (EPDM, NBR and others). Polymers as main compounds of plastic materials are safe for human health. However, the remains of unreacted monomer and modified additives
can be volatile and toxic. Modifiers usually in the form of low molecular weight compounds can penetrate from the plastic to the water and deteriorate its quality, thus providing nutritional compounds for microbes in tap water. Among the huge amount of rubber compounds the largest part of the sanitary products are those made of EPDM and NBR. They are characterized by a high chemical resistance including a resistance to atmospheric agents. They meet the specific requirements associated with the flow of hot water (high temperature resistance), especially in the case of EPDM and low deformation, which translates into prolonged use. Unfortunately, materials like rubber compounds and polymers contacting with drinking water may cause the secondary pollution both, chemical and microbiological.
All tests were performed using two control reference materials. Positive control (susceptible to biofilm formation) was glass plate coated with paraffin wax layer. Negative control (unsusceptible to biofilm formation) was plate made of stainless steel.
Continuous flow reactor
Specific reactors - UPE (Polish specific name) supplied from cold tap water were used in this investigation (Figure 1). The cylindrical body of UPE (inside diameter was 150 mm, high was 550 mm) was made of high quality stainless steel with Teflon seal. On top of the reactor was a removable cover with a venting valve. Water inflow tube was made of Teflon and water pressure was regulated by a ball valve. Inside the reactor, at the bottom, a conical diffuser with two partitions was located. A special sample stand made of stainless steel was placed in vertical position inside the cylinder. The water outflow with water meter was located on the side of the UPE about 50 mm below the top. The water flow proceeded from the bottom to the top of reactor so that the reactor could be filled with water evenly and flow direction was protected against the mixing of inlet and outlet water.
The testing method applied in the Department of Environmental Hygiene Laboratory of NIH-NIPH involves the measure of bioluminescence level in swabs taken from the surface of material contacting with drinking water by using luminometer. Exposition of tested material lasts from eight (polymers) to ten weeks (rubber) and is performed inside the continuous flow reactor (UPE) in conditions of dynamic water flow. The crucial element of the testing method is the fact, that all living cells include the universal chemical compound - adenosine triphosphate (ATP) which functions as a carrier of free energy. This energy is used in most of the life processes requiring the energy input. During biochemical reaction of enzymatic decomposition of ATP energy is emitted in form of light (bioluminescence). The measure of this energy enables indirect assessment of ATP concentration in swab sample taken from the surface of tested material.
HY-LiTE® (MERCK) test systems to in vivo application were used to bioluminescence level measures. The test system consists of hygiene swabs free of ATP and the “pens” with proper dose of liquid reagents to dilution, buffering and neutralization of the sample, as well as lyophilisate of reaction complex luciferin-luciferase. This test system was adapted to operate with luminometer HY-LiTE 2® (MERCK).
The sensitivity of applied tests was 1,4 x 10-14 mols
ATP.
RESULTS
The tests results on biofilm formation process for various types of materials intended for contact with drinking water from different producers were presented in Tables 1, 2 and 3.
Ten different products made of polyvinyl chloride intended to contact with drinking water were tested and evaluated. The results obtained for all PVC samples were similar (Table 1). In each case values expressed in RLU/cm2 did not exceed the acceptable
limit determined pursuant to ten-time values observed on the negative control surface (10 x K-). Sample number 5 characterized the highest bioluminescence values, however the values were below acceptable limit during full time of investigation. In all cases
presented above, examined materials obtained positive test assessment, what confirmed their proper quality and resulted in issuing of the Hygienic Certificate and further marketing authorization in Poland.
Results for tested seven different products made of polypropylene from different producers are presented in Table 2. The bioluminescence level on the surface of six of them was low (<500 RLU/cm2). In case of
one material (sample 2) the bioluminescence level, measured in the measuring period, exceeded slightly 2000 RLU/cm2, however the negative control sample,
tested in parallel, showed results 253 RLU/cm2. Thus,
working on the assumption of the assessment criteria for the method (10 x K-), enabled to positive assessment of this material sample made of polypropylene. All samples made of polypropylene obtained positive test assessment, what confirmed their proper quality and resulted in issuing of the Hygienic Certificate and further marketing authorization for direct contact with water intended for human consumption.
Ten different products intended to contact with drinking water and made of polyethylene from different producers were tested. The results for all samples presented above were similar (Table 3). In case of eight of them, during eight week examined period, the bioluminescence was observed on the level very close to negative control, so in the range from Figure 1. Continuous flowing reactor’s diagram. a – steel cylinder, b – samples stand, c – water inflow, d – water outflow, e – diffuser, f – water meter, g – sample of material intended to contact with water.
approximately 100 RLU/cm2 to 300 RLU/cm2. In three
cases (samples no. 3, 4 and 10) the values obtained were higher and amounted above 1000 RLU/cm2.
They still did not exceed the unacceptable value limit.
All examined polyethylene materials obtained positive test assessment, what confirmed their proper quality and resulted in issuing of the Hygienic Certificate and further marketing authorization in Poland.
Table 1. Bioluminescence on the surface of different polyvinyl chloride (PVC) materials expressed in RLU*/cm2
PVC Subsequent weeks of the study
0 I II III IV V VI VII VIII
sample 1 limit value** 17036 358750 1100721 1350900 1410800 1630870 1540950 1490970 10901510 sample 2 limit value 14018 65029 105039 225029 92062 1250175 1020457 321950 125820 sample 3 limit value 13029 145093 77065 188085 2010142 2070162 1540150 1120127 110790 sample 4 limit value 31020 1100159 1620107 1160187 225720 1210188 1420153 1350137 147073 sample 5 limit value 30021 1100155 171810 1400166 266610 750411 1000633 670870 600900 sample 6 limit value 37019 66056 121089 210074 2580151 3090234 2740287 3660211 3530178 sample 7 limit value 14019 80067 125098 1600165 1400170 260850 210910 1110180 160780 sample 8 limit value 9011 33045 56090 125800 1000160 1200230 1450250 1600240 1700260 sample 9 limit value 12011 45056 80094 144900 1320187 1600156 1650210 1910183 1800162 sample 10 limit value 1209 45040 80066 90097 1320110 1600121 1650106 1910120 1800115 * - Relative Light Units
** - acceptable limit of RLU/cm2 determined pursuant to ten-time values observed on the negative control surface (10 x K-) Table 2. Bioluminescence on the surface of different polypropylene materials expressed in RLU/cm2
PP Subsequent weeks of the study
0 I II III IV V VI VII VIII
sample 1 limit value 37029 66095 1210134 2100195 2580254 2090312 2340378 2660472 2530456 sample 2 limit value 37030 150660 1210317 10002100 13562580 13892090 23892340 21002660 24332530 sample 3 limit value 37037 156660 1210140 2100143 2580158 3090165 2740156 3660147 3530166 sample 4 limit value 37029 66098 1210123 2100167 1950197 2210211 2740356 3000287 2470311 sample 5 limit value 14025 65025 105026 225057 248920 125048 1020350 190950 160820 sample 6 limit value 31037 1100170 1620110 1160120 138720 1210145 1420126 1350147 1470136 sample 7 limit value 1209 45064 159800 264900 1320350 1600445 1650474 1910450 1800463
Table 3. Bioluminescence on the surface of different polyethylene materials expressed in RLU/cm2
PE 0 I II Subsequent weeks of the studyIII IV V VI VII VIII
sample 1 limit value 30037 1110180 130980 1330140 138810 175750 156930 127960 146740 sample 2 limit value 23036 106560 182890 1740274 1470286 1620311 1850246 1770198 1810233 sample 3 limit value 37030 130660 1210217 2100736 14162580 30901311 23672740 19763660 21333530 sample 4 limit value 15021 35097 196220 900311 1640560 1870710 1680900 2100732 11621640 sample 5 limit value 17025 100075 1520110 1700166 1650148 1480136 1800250 1300121 100950 sample 6 limit value 17025 100064 1520134 1700157 1650183 1480155 1800110 1300124 131950 sample 7 limit value 19034 48058 1200132 1110167 190980 1300210 1570150 110900 102840 sample 8 limit value 30032 45077 63086 90074 103800 120094 1100124 1000151 133930 sample 9 limit value 17032 3130303 2830433 3720457 8670683 3470225 3920203 5480165 8980177 sample 10 limit value 37030 150660 1210317 10002100 13562580 13893090 23892740 21003660 24333530 Table 4. Bioluminescence on the surface of different rubber materials expressed in RLU/cm2
Rubber 0 I II III Subsequent weeks of the studyIV V VI VII VIII IX X sample 1 limit value 37 300 1110262 1373980 36331330 5283810 13133750 12666930 13000960 137831330 126661240 111661110 sample 2 limit value 15 150 25060 22051 1354560 2400810 4297700 5711960 4963900 53421200 51401200 53361330 sample 3 limit value 42 330 360870 11001000 31001230 4955790 10906133 56782300 42002370 34001900 37002000 32632230 sample 4 limit value 37 470 262980 373370 2633530 52831310 231661160 12666850 3000960 137833180 126442310 131212090 sample 5 limit value 14 120 746760 16661220 14332590 3170950 2730846 1430963 11172110 10633630 4000945 10223890 sample 6 limit value 19 140 470800 31001250 75001600 106001400 12300850 12150910 112001110 11630780 10700980 10500930 sample 7 limit value 13 70 1750650 46001410 137002100 161003600 195003900 253004800 280004500 291005100 330006100 313005500 sample 8 limit value 12 90 654450 1890630 37501140 65701500 15608590 91001680 96001700 95001680 119001520 123001460 sample 9 limit value 10 90 850330 3600560 7800800 85001000 12007900 91001450 89001600 95001700 124002200 145003100 sample 10 limit value 13 120 900940 15401090 18001300 22001740 16902230 21602200 23002000 25001900 23502300 24002500
Ten samples made of rubber compounds intended to contact with drinking water were tested. All of them were intended for production of seals and flexible hoses. The testing period was prolonged to ten weeks, what enabled more precise observation of dynamic changes of bioluminescence level determined in swabs coming from the samples surface. Only in two cases (samples no. 5 and 10) the assessment of the material proceeded without reservations. The bioluminescence values from the surface of the remaining 8 samples were significantly higher than analogical values from the surfaces of polymeric materials (PE, PP and PVC). In the course of the results interpretation the application of the final product, was taken into consideration, including the area of the materials surface, which contacts with drinking water in the real application. In case of the products like sealing and rubber pads this surface is usually of the minimal degree and possible microbial growth covers only the connection points inside the installation sealed with these materials. Despite these materials did not meet the requirements for materials contacting with drinking water they were conditionally allowed for that particular kind of application. In cases when the rubber compound was destined for flexible hoses production – the product with significantly larger surface contacting with drinking water than sealing elements – the samples did not obtain positive assessment and they were not allowed to contact with water intended for human consumption.
DISCUSSION
All tested samples of polymeric materials (polypropylene, polyethylene, polyvinyl chloride) demonstrated a low susceptibility to the biofilm formation. The bioluminescence from their surface were within the predetermined acceptable limits, which means they did not exceed ten times the level of bioluminescence determined in swabs taken from the negative control surface. Despite that fact, in some cases, a temporary growth of determined values was observed, which could be related to the migration of the substances like stabilizers and hardeners added to products during their production from the material’s surface. These substances may be a potential source of organic carbon for microorganisms, resulting in enhanced growth of their numbers on the materials surface. The studies conducted by Traczewska and
Sitarska [31] also confirmed that the materials of this
type due to the emission of the substances stimulating the growth of microorganisms may be susceptible to biofilm formation, and because of that fact, their use in new water supply networks does not provide protection against secondary microbial contamination and corrosion. This particular fact is important in case
of the use of poor quality materials characterizing by high emissions of organic substances. The possibility of appearing in the water network microorganisms, that are capable of metabolic degradation of the polymers should additionally be taken into account. However, such a phenomenon occurs at the moment of formation of the biofilm mature form, which is frequently related to poor quality of the material, which contributes to the promotion of microbial colonization of its surface [8].Also, comparison of the results of the assessment of various organic materials susceptibility, obtained by using a parallel classical microbiological techniques, indicates such character of the most of the polymeric products and materials [1]. However, it should be taken into consideration, that only a small part of this type of materials available on the market was tested. Among them, it can be stated a considerable variety of additives purposed to prolong the life of polymers (plasticizers), giving them a specific physicochemical properties (stabilizers), and other chemical compounds such as dye additions. Each of these substances undergo a migration from the material into the water inside the installation, which can be a potential source of nutrients for microorganisms [24].
The second group of tested materials was rubber, which is generally used for production of sealing elements in fittings and other products in contact with drinking water. Due to complex chemical composition, as well as a very large number of organic additives, which undergo intensive migration to the water, the materials from this group represent usually the largest percentage among all materials and products evaluated negatively. A final assessment of those materials was expanded to include fact, that the sealing elements are usually small in size and their contact with water inside the network is very limited. In spite of this, only two of the tested rubber materials samples have been evaluated without reservations as appropriate to contact with drinking water. In all other cases, the materials were evaluated negatively. In one case, the regular supplier of raw material (a blend of EPDM) has changed its chemical composition without informing about that fact of the manufacturer of the final product. Changes in the chemical composition caused the increased emission of organic substances, which enhanced the growth of microorganisms on the product`s surface, manufactured from raw material of inadequate quality.
Bressler et al. [2] in their study also included the blend of EPDM to materials, which promote the growth of microorganisms, and biofilms formed on the surface of products from these materials which caused secondary microbial contamination of the water network, and additionally might constitute a reservoir of potentially pathogenic bacteria for instance
published Kilb et al. [11], who described the parts of the installation made of soft rubber materials such as EPDM or NBR as a potential source of secondary microbial contamination of the network inside the building. This is also confirmed by the results of the tests comparing the number of microorganisms in the network supervised by the water producer before it is delivered to the consumer and at the consumer’s directly. Pepper et al. [28] observed that microbiological contamination of water is generally higher in water samples collected from the consumer, which is the result of the indoor plumbing materials, which promote the growth of microorganisms.
Biofilm formation on materials used for distribution and storage of water intended for human consumption is determined by many factors. Among them the main role play complex relations between water quality and the way of its treatment, and the technical and operating conditions of water distribution systems. The specific technical and chemical properties of the materials and construction products used in the water network are one of the factors that could significantly affect the increase of the phenomenon. The assessment of organic materials used in the storage and distribution of water with regard to their susceptibility to biofilm formation is important for practical reasons. This phenomenon should be taken into consideration in the process of hygienic evaluation of the materials prior to their use in practice. It can be helpful for reducing the scale of the risk associated with biofilm formation and, as a consequence, inadequate microbiological quality of water consumed.
CONCLUSIONS
1. Significant susceptibility to biofilm formation in the group of products made of rubber compounds, including NBR and EPDM compounds, was found. 2. Tested polymeric materials such as polyethylene,
polyvinyl chloride, polypropylene, except for several cases, do not revealed susceptibility to biofilm formation.
3. Application of polymer materials for distribution of water intended for human consumption does not fully protect water from secondary microbiological contamination.
4. Further assessment of materials and products contacting with water intended for human consumption is necessary in terms to their susceptibility on biofilm formation.
Acknowledgement
This work was financed by the National Institute of Public Health - National Institute of Hygiene, Warsaw, Poland.
Conflict of interest
The authors declare no conflict of interest.
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Received: 25.04.2016 Accepted: 25.08.2016
